The Butler Family Letters are a collection of 70 original letters written between 1835 and 1863 by some of the pioneers who settled in Polk County, Oregon, and founded Monmouth University (now Western Oregon University).

The letters were written by Peter and Rachel Butler's family and friends who left Monmouth, Illinois, in 1853 to cross the Oregon Trail and settle in Polk County, Oregon, along with other members of the Disciples of Christ Church. Their primary goal was to settle a new community, which they named Monmouth in honor of their original home in Illinois. Peter Butler’s eldest son, Ira F.M. Butler, and his son-in-law Thomas Hutchinson were two of the original eleven charter signers who in 1856 officially established Monmouth University. The Disciples of Christ Church and Monmouth University shared the same building until 1871.

The Butler Family Letters describe the challenges of daily life faced by Oregon's early pioneers. The letters describe farming and agriculture, living, death, birth, illness, homesickness, economic impact of goldmine discoveries, settler conflicts with Native Americans and how the Oregon Territory was influenced by national politics.

The collection of letters was donated to Western Oregon University Archives in 1993 by Dr. Lawrence Butler of Atchison, Kansas. Some of the letters were transcribed in 1976 and independently published as Letters from Polk County, Oregon to Monmouth, Illinois 1853-1863. This digital collection was published in 2013 by university archivist Erin Passehl and graduate student intern Brittney Teal-Cribbs. Previous web-based iterations of the Butler Family Letters were created by Kathleen Casey, Karen Head, Lotte Larsen and Roy Bennett.